1. Field of the Invention
The invention concerns a pressurized can, the body of which is a cylinder, with a preferably pushed-in bottom, a dome-like top section with a valve to expel the can contents consisting of product component and propellant, and which has a floating plunger mounted on the interior wall of the cylinder, which separates the propellant gas chamber from the product component and which has a cavity in its upper side. The pressurized can is particularly suited for the expulsion of building foams, for instance single-component polyurethane foams, such as those commonly used for construction and sealing purposes.
2. Description of the Related Art
Such pressurized cans are used to expel different products. These include sealants on a rubber, oil, butyl, silicon and acrylate basis, but especially foaming agents based on polyisocyanate prepolymers. On contact with water (humidity), such polyisocyanate prepolymers turn into polyurethane foams which are used for sealing, filling, insulation, adhesion and fastening, especially in the construction industry. The pressurized cans to expel such foaming agents on a polyisocyanate basis are usually made of sheet steel, because of the great interior pressure among other reasons, and special valves are used to facilitate the handling of the can contents.
Pressurized cans of this type are known, for instance, from U.S. Pat. No. 3,362,589. When used for the production of polyurethane foams, such pressurized cans contain a filling consisting of, for example, 60% by weight polyurethane prepolymers, and about 40% by weight propellant gas. The greater part of the propellant gas is used as a transporting agent, to expel the prepolymer from the pressurized can. Only a small portion of the propellant gas, about 10%, turns into a foaming agent and supports expansion.
If the can is stored for a longer period of time, the component substances usually separate, in which case the specifically heavier propellant settles on the bottom of the pressurized can. Before use, it is advisable to shake the can forcefully and for a long time to achieve the intensive mixture of foaming agent and propellant. Insofar as the gas works as a propellant and comes out of the pressurized can with the foaming agent, it escapes into the atmosphere under expansion.
EP-A 0 078 936 describes a pressurized can for the expulsion of building foams, the body of which is a cylinder, with a preferably pushed-in bottom and a dome-like top section with a seal. A valve for expelling the can contents consisting of a propellant and foaming agent is placed in the dome-like top section. A floating plunger is mounted on the interior wall of the body cylinder between the propellant and the foaming agent contained in different chambers of the can which separates the lower propellant gas chamber from the chamber above it which contains the foaming agent. As the can empties, the plunger moves up within the can, stopping against the dome-like top section of the pressurized can when finally empty. To ensure thorough emptying, the top of the plunger is shaped to fit the curvature of the can dome, and has a cavity in the area where the valve disk reaches down into the inside of the can. According to EP-A 0 078 936, the plunger is fitted into the can cylinder in such a way that propellant can pass between the wall of the can and the pressurized can from the propellant chamber into the foaming agent chamber, but the foaming agent essentially remains in its upper chamber.
Pressurized cans of the type described in EP-A 0 078 936 have proven themselves very well in practice. They make it possible to use up the foaming agent to a great extent, so that only very small quantities of foaming agent remain when the can is fully empty. These small quantities fall within the range of about 5% of the original can contents. The disadvantage, however, is that the polyisocyanate prepolymers used as foaming agent[s] are highly reactive and toxic. For this reason, even empty pressurized cans cannot be disposed of easily, but require special handling pursuant to the regulations applicable to such residues. This leads to considerable drawbacks and costs. The same applies to a number of other products which are sold in cans and which are highly reactive and/or toxic.